ECR (very-long-chain enoyl-CoA reductase; also ECERIFERUM10/CER10, AtTSC13, AOD2; At3g55360) is the enoyl reductase of the endoplasmic reticulum fatty acid elongase in Arabidopsis and the ortholog of yeast TSC13 and animal TECR. A member of the steroid 5-alpha-reductase-like family, it is a multi-pass integral ER membrane protein distributed uniformly over the ER. ECR catalyzes the fourth and final step of each very-long-chain fatty acid (VLCFA) elongation cycle, the NADPH-dependent reduction of trans-2,3-enoyl-CoA (produced by the dehydratase PAS2, with which it interacts) to a saturated acyl-CoA two carbons longer than the primer. As a shared, broadly expressed elongase subunit it participates in all VLCFA elongation reactions, supplying VLCFAs for cuticular waxes, seed triacylglycerols and sphingolipids. cer10 mutants are glossy (reduced wax), have altered sphingolipid and seed VLCFA composition, and show reduced organ size, organ fusion and defective cell expansion and endocytic trafficking attributed to abnormal sphingolipids; unlike KCR1 and PAS2 null mutants they are viable.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:30604175 Arabidopsis Bax inhibitor-1 interacts with enzymes related t... | REMOVE | Summary: Interaction/co-purification of CER10/ECR with AtELO2, cytochrome b5 and AtBI-1. Reason: Generic 'protein binding' is uninformative; the reported interactions reflect ECR's membership of the ER elongase assembly, which is captured by the fatty acid elongase complex term. Removal does not dispute the interactions. Supporting Evidence: PMID:30604175 AtELO2 and AtCb5-B also interact with KCR1, PAS2, and CER10, which are essential for the synthesis of VLCFAs. |
| GO:0005783 endoplasmic reticulum | HDA PMID:16618929 Mapping the Arabidopsis organelle proteome. | ACCEPT | Summary: LOPIT organelle proteomics (Dunkley et al. 2006) assigned ECR to the ER. Reason: Consistent with focused GFP-ECR localization. Supporting Evidence: PMID:16618929 enabling confident and simultaneous localization of 527 proteins to the endoplasmic reticulum, Golgi apparatus, vacuolar membrane, plasma membrane, or mitochondria and plastids PMID:15829606 the GFP fluorescence labeled a reticulate network typical of the ER in all examined organs |
| GO:0005783 endoplasmic reticulum | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | ACCEPT | Summary: LOPIT proteomics (Nikolovski et al. 2012) assigned ECR to the ER. Reason: Consistent with focused localization. Supporting Evidence: PMID:22923678 we identified the subcellular localization of 1,110 proteins with high confidence PMID:15829606 the GFP fluorescence labeled a reticulate network typical of the ER in all examined organs |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference of ER activity for the TECR/TSC13 clade (PTN000059180). Reason: Correct; ECR has been directly localized to the ER. Supporting Evidence: PMID:15829606 the GFP fluorescence labeled a reticulate network typical of the ER in all examined organs |
| GO:0005789 endoplasmic reticulum membrane | IDA PMID:15829606 Disruptions of the Arabidopsis Enoyl-CoA reductase gene reve... | ACCEPT | Summary: A functional GFP-ECR fusion (complementing cer10) labels the ER network, co-stains with an ER dye and outlines fusiform bodies, and is uniformly distributed on the ER membrane. Reason: Core localization. Supporting Evidence: PMID:15829606 the GFP fluorescence labeled a reticulate network typical of the ER in all examined organs PMID:15829606 confirming that GFP-ECR is localized to the ER membrane |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (ER membrane, multi-pass). Reason: Correct. |
| GO:0005829 cytosol | HDA PMID:28887381 Global Analysis of Membrane-associated Protein Oligomerizati... | MARK AS OVER ANNOTATED | Summary: High-throughput protein correlation profiling assigned ECR to a cytosolic pool. Reason: ECR is a multi-pass integral ER membrane protein; a soluble cytosolic assignment from large-scale co-fractionation is not supported by focused localization of a functional GFP fusion. Supporting Evidence: PMID:28887381 Over 150 proteins had a complicated localization pattern PMID:15829606 confirming that GFP-ECR is localized to the ER membrane |
| GO:0006629 lipid metabolic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the steroid 5-alpha reductase/TECR domain to lipid metabolism. Reason: Correct but general. |
| GO:0006633 fatty acid biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: UniPathway mapping to fatty acid biosynthesis. Reason: Correct but general; the informative process is VLCFA biosynthesis. |
| GO:0006665 sphingolipid metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference of involvement in sphingolipid metabolism for the TECR clade. Reason: ECR supplies the VLCFA moieties of sphingolipids; cer10 mutants have altered sphingolipid VLCFA composition, and yeast/animal orthologs are required for sphingolipid synthesis. Supporting Evidence: PMID:15829606 The absence of ECR activity results in a reduction of cuticular wax load and affects VLCFA composition of seed triacylglycerols and sphingolipids |
| GO:0006665 sphingolipid metabolic process | IMP PMID:15829606 Disruptions of the Arabidopsis Enoyl-CoA reductase gene reve... | ACCEPT | Summary: cer10 mutants have altered sphingolipid VLCFA composition, proposed to underlie their cell-expansion defects. Reason: Supported by the lipid analyses; ECR contributes the VLCFA acyl chains of ceramides and complex sphingolipids. Supporting Evidence: PMID:15829606 The absence of ECR activity results in a reduction of cuticular wax load and affects VLCFA composition of seed triacylglycerols and sphingolipids PMID:15829606 suggesting that the developmental phenotypes arise from abnormal sphingolipid composition |
| GO:0009922 fatty acid elongase activity | IMP PMID:15829606 Disruptions of the Arabidopsis Enoyl-CoA reductase gene reve... | MODIFY | Summary: GOA uses 'fatty acid elongase activity' for ECR based on the cer10 mutant; however GO:0009922 is defined as the condensation (KCS) step of the elongation cycle. Reason: ECR catalyzes the fourth (enoyl-CoA reduction) step of the cycle, not the condensation that GO:0009922 now denotes. The correct activity term is very-long-chain enoyl-CoA reductase activity (GO:0102758), already present via IBA/IEA. Proposed replacements: very-long-chain enoyl-CoA reductase activity Supporting Evidence: PMID:15829606 ECR is an enzyme that catalyzes the last step of VLCFA elongation, reduction of the enoyl-CoA, in eukaryotic cells. PMID:14673020 heterologous expression of At3g55360 functionally complements the temperature-sensitive phenotype of a yeast tsc13 mutant that is deficient in enoyl reductase activity |
| GO:0009923 fatty acid elongase complex | TAS PMID:15829606 Disruptions of the Arabidopsis Enoyl-CoA reductase gene reve... | ACCEPT | Summary: ECR is the enoyl reductase subunit of the ER fatty acid elongase; the Arabidopsis protein interacts with the yeast condensing enzymes Elo2p/Elo3p and with PAS2 in planta. Reason: Membership of the elongase complex is supported by physical interaction data. Supporting Evidence: PMID:14673020 AtTSC13 is shown to interact physically with the Elo2p and Elo3p components of the yeast elongase complex PMID:18799749 PAS2 was specifically associated in the endoplasmic reticulum with the enoyl-CoA reductase CER10, the fourth enzyme of the elongase complex |
| GO:0010025 wax biosynthetic process | IMP PMID:15829606 Disruptions of the Arabidopsis Enoyl-CoA reductase gene reve... | ACCEPT | Summary: cer10 (ecr) mutants are glossy with reduced cuticular wax load, and epidermis-specific ECR silencing reduces wax. Reason: ECR catalyzes a step in the synthesis of the VLCFA precursors of all cuticular wax components. Supporting Evidence: PMID:15829606 The absence of ECR activity results in a reduction of cuticular wax load and affects VLCFA composition of seed triacylglycerols and sphingolipids PMID:15829606 demonstrating in planta that ECR is involved in all VLCFA elongation reactions in Arabidopsis |
| GO:0010025 wax biosynthetic process | IMP PMID:1847001 Chrysotile asbestos and health in Zimbabwe: I. Analysis of m... | ACCEPT | Summary: Wax biosynthetic process for ECR/CER10 attributed to PMID:1847001, which resolves to an unrelated occupational-health paper on chrysotile asbestos in Zimbabwe. Reason: The biological assertion (ECR/CER10 is required for wax biosynthesis) is correct and independently supported by PMID:15829606. The cited identifier is wrong (probably a legacy TAIR mapping of the Koornneef et al. 1989 eceriferum mutant description, which has no PMID); the reference should be corrected upstream. Supporting Evidence: PMID:15829606 The absence of ECR activity results in a reduction of cuticular wax load and affects VLCFA composition of seed triacylglycerols and sphingolipids PMID:15829606 The cer10 mutant was originally isolated because of its glossy stem phenotype indicative of decreased cuticular wax accumulation |
| GO:0010091 trichome branching | IMP PMID:24014871 Arabidopsis GLASSY HAIR genes promote trichome papillae deve... | KEEP AS NON CORE | Summary: glh6/cer10 mutant trichomes form fewer branches. Reason: A downstream morphological consequence of defective VLCFA synthesis and cell expansion rather than a direct role in trichome branching. Supporting Evidence: PMID:24014871 On average, trichomes on glh1, glh2, and glh6 leaves formed fewer branches. PMID:15829606 they appeared to have short, crooked, and abnormally swollen stalks and branches |
| GO:0016627 oxidoreductase activity, acting on the CH-CH group of donors | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping to CH-CH oxidoreductase activity. Reason: Correct parent of very-long-chain enoyl-CoA reductase activity. |
| GO:0042761 very long-chain fatty acid biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference of involvement in VLCFA biosynthesis. Reason: Core process. Supporting Evidence: PMID:15829606 demonstrating in planta that ECR is involved in all VLCFA elongation reactions in Arabidopsis |
| GO:0102758 very-long-chain enoyl-CoA reductase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference of very-long-chain enoyl-CoA reductase activity from the TECR/TSC13 clade (yeast TSC13, human TECR). Reason: Core activity; supported by complementation of the yeast tsc13 enoyl reductase mutant. Supporting Evidence: PMID:14673020 heterologous expression of At3g55360 functionally complements the temperature-sensitive phenotype of a yeast tsc13 mutant that is deficient in enoyl reductase activity PMID:14673020 At3g55360 apparently encodes the sole enoyl reductase activity associated with microsomal fatty acid elongation in Arabidopsis |
| GO:0102758 very-long-chain enoyl-CoA reductase activity | IEA GO_REF:0000120 | ACCEPT | Summary: EC 1.3.1.93/RHEA mapping. Reason: Correct. |
| GO:0160062 cutin-based cuticle development | IMP PMID:24014871 Arabidopsis GLASSY HAIR genes promote trichome papillae deve... | KEEP AS NON CORE | Summary: glh6/cer10 leaves and trichomes are permeable to toluidine blue, indicating a defective cuticle. Reason: ECR contributes VLCFA precursors of cuticular lipids; cuticle development is an indirect consequence. Supporting Evidence: PMID:24014871 We found that glh6 mutant trichomes and leaves were stained with TB PMID:24014871 the glh6 mutants showed defects in leaf cuticular wax, and glh6 was found to represent a new allele of the eceriferum 10 (cer10) mutation |
| GO:1905499 trichome papilla formation | IMP PMID:24014871 Arabidopsis GLASSY HAIR genes promote trichome papillae deve... | KEEP AS NON CORE | Summary: glh6/cer10 trichomes show reduced and variable papillae. Reason: The authors themselves suggest the papillae defect may be an indirect consequence of developmental arrest; not a core function. Supporting Evidence: PMID:24014871 suggesting that papillae formation defects in the glh6 mutant trichomes may be an indirect consequence of developmental arrest at various stages |
Loading supporting content…
Download this section (compressed HTML)Q: Why is loss of ECR/CER10 viable in Arabidopsis whereas loss of KCR1 or PAS2 is embryo lethal? Which enzyme (e.g. a steroid 5-alpha-reductase-like paralog) provides residual enoyl-CoA reductase activity?
Q: Do the cell-expansion and endocytic trafficking defects of cer10 arise specifically from altered sphingolipid acyl-chain length, and which sphingolipid species are responsible?
Experiment: Measure residual microsomal enoyl-CoA reductase activity and enoyl-CoA intermediates in cer10 null mutants, and test candidate paralogs by yeast tsc13 complementation and higher-order mutant analysis.
Experiment: Rescue cer10 with epidermis-, seed- or sphingolipid-relevant tissue-specific promoters and profile sphingolipid species to link specific VLCFA-containing lipids to the cell-expansion phenotype.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)